1. Field of the Invention
The present invention relates to a wiper apparatus for vehicles and, more particularly, to a wiper apparatus for vehicles in which the pressing force pressing a wiper blade against a window pane is adjustable.
2. Description of the Related Art
As shown in FIG. 3, a conventional wiper apparatus for vehicles is comprised of a wiper blade 6 for wiping the surface of a window pane 6a, a wiper arm 3 rotatably supporting the wiper blade 6 through a pin 3a, and a driving arm 2 connected to the wiper arm 3 through a pivoting pin 5 at one end thereof. The other end of the driving arm 2 (not shown) is operatively connected to a motor 1 for oscillating the wiper arm 3. A tension coil spring 4 disposed between the wiper arm 3 and the driving arm 2 pivots the wiper arm 3 around the pivoting pin 5 to bias the blade 6 towards the front surface of the window pane 6a. The blade 6 wipes the front surface of the window pane 6a when the motor 1 operates the driving arm 2.
Air flows along the front surface of the window pane 6a which lifts the blade 6 against the biasing force of the tension coil spring 4. Further, the velocity of air flow changes in accordance with the vehicle speed. If a weak biasing force tension coil spring 4 is used, the blade 6 will be forced away from the front surface of the window pane at high vehicle speeds and wiping cannot be sufficiently carried out. If a tension coil spring 4 with a strong biasing force tension is used so as to eliminate lifting of the blade 6, the blade 6 is pressed too hard against the front surface of the window pane 6a and chattering may occur at low vehicle speeds.